Vehicles may use a vacuum pump to provide negative pressure to drive various features of an internal combustion engine. For example, a vacuum may be utilized to drive various actuators coupled to various systems and/or engine components such as cabin climate controls, a braking system with pneumatic boost, front axle engagement for a four wheel drive system, wastegate valves, compressor bypass valves, intake manifold air control valves, and/or other systems and accessories. Further, a vacuum may be used for crankcase ventilation, vacuum leak-down testing, and fuel vapor purging.
For example, US 2008/0103667 describes a negative pressure control apparatus that allows for a vehicle braking operation. The system includes a throttle valve in each branched intake air passage for supplying air to respective engine cylinders. Each of the throttle valves are linked to a common shaft so that the throttle valves integrally rotate as a collective unit. The apparatus also includes an air ejector that functions as a vacuum pump to drive the negative pressure generated downstream from the throttle valves. Further, the apparatus includes a communication passage to provide a passage for the negative pressure to a brake booster.
The inventors herein have recognized various issues with the above system. In particular, the negative pressure control apparatus can only generate a vacuum at low engine load. Since each intake passage includes a throttle valve that is also responsible for adjusting the intake air for each cylinder, at high engine load, increasing the intake air for combustion takes precedence over decreasing the throttle angle for generating a vacuum. Therefore, vacuum cannot be generated at high engine load using the negative pressure control apparatus described in the above identified patent application. Further, an electrical control unit (ECU) is coupled to the negative pressure control apparatus to actuate the common shaft during low engine load to generate vacuum.
As such, one example approach to address the above issues is to throttle less than all cylinders to generate a vacuum such that vacuum can be generated regardless of the engine operating condition. For example, by utilizing an engine with both a main throttle to regulate intake air to a plurality of cylinders and a port throttle to adjust the airflow to one cylinder, a vacuum can be generated at any engine operating condition, including low engine load and high engine load. In this way, one cylinder downstream from the port throttle may function as both a combustion cylinder, and nominally, as a vacuum pump, in some embodiments. By using the cylinder as the vacuum pump, it is possible to generate a vacuum without including a traditional vacuum pump; however a vacuum pump may be included, if desired. As such, due to the dual functionality of the cylinder the engine weight may be reduced.
Further, the vacuum system may be a self-sustaining vacuum system that functions independently from an ECU. Specifically, the vacuum system may generate a vacuum downstream from the port throttle and capture the vacuum within a reservoir. This configuration enables the reservoir to distribute the vacuum to various vacuum consumers. Further, by taking advantage of pneumatically linking the reservoir to a vacuum actuator responsible for adjusting the port throttle of the one cylinder, a pressure state of the vacuum reservoir serves as a driving force for the vacuum actuator. In this way, it is possible to achieve a vacuum system driven by pneumatics rather than relying upon sensors to transmit electronic signals for actuation.
Note that various valves may be utilized to further direct airflow. Further, the self-sustaining vacuum system may include one or more sensors to evaluate the airflow downstream from the port throttle, if desired.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.